A printhead assembly of an inkjet printer has a plurality of inkjets from which drops of ink are ejected towards the recording medium. A printer may have multiple print heads which are similar or may be identical. The inkjets of a printhead receive the ink from an ink manifold in the printhead which, in turn, receives ink from an ink supply source, such as a melted ink reservoir or an ink cartridge. Ink supply volume sensing is employed with various ink types and states. The largest volume of ink in a phase change ink device is typically in the solid state and is melted as needed. Each inkjet includes a channel having one end connected to the ink supply manifold. The other end of the ink channel has an orifice, or nozzle, for ejecting drops of ink. The inkjets may be formed in an aperture, or nozzle plate that has openings corresponding to the nozzles of the ink jets. During operation, firing signals excite actuators in the inkjets to expel drops of fluid from the inkjet nozzles onto the recording medium. By selectively exciting the actuators of the ink jets to eject drops as the recording medium and/or printhead assembly are moved relative to each other, the deposited drops can be precisely patterned to form particular text and graphic images on the recording medium.
Previously known systems typically were configured to detect or track the amount of ink available for delivery to the printhead(s). For example, in some previously known phase change ink systems, when the amount of remaining ink in the ink supply source, typically in the solid state, becomes equal to or less than a predetermined “low ink” set point, a “low ink” notification is generated that alerts a user to the low ink status so that the user may take appropriate action such as replenishing the ink supply and/or ordering new quantities of ink. Printing operations may typically continue after a low ink notification is generated. When most or substantially all of the deliverable ink has been depleted, an “ink out” notification is generated to alert the user that ink is no longer available for one or more printheads.
In previously known systems, “ink low” and “ink out” set points are typically predetermined by sensor placement where low and out states correspond directly to the non adjustable sensor actuation point. A variant of the sensor actuation fixed transition point was to add a “volume consumption” delay prior to issuing notification of a low or out condition. This fixed value was programmed into the print controller or stored in memory for access by the print controller during manufacture of the system. This situation does not provide flexibility in the number of images or prints that remain at the time the available ink volume reaches the predetermined “ink low” set point. For example, indicating an ink low status when there is a relatively large volume of ink remaining in an ink source may cause a user to replenish and/or purchase ink more often than is desired. Similarly, indicating an ink low status fairly close to the “ink out” set point may leave a user with an inadequate amount of time to replenish and/or purchase the ink before printing operations are halted. Large print jobs may have to be discontinued while replacement ink is obtained. In addition, the fixed, predetermined “low ink” set point may not be appropriate for customers that either print very little or that have high monthly print volumes.